Rodriguez is a 22-year-old prospect who went 7-7 with a 4.23 ERA for Double-A Reading last year, allowing 121 hits and 76 walks with 136 strikeouts over 134 innings. He is expected to start the season with Double-A Bowie.

"He has all the ingredients you look for in a young pitcher -- size, arm, stuff," executive vice president of baseball operations Dan Duquette said of Rodriguez. "And he has the results, also."

The 6-foot-4, 200-pound Rodriguez pitched in the SiriusXM All-Star Futures Game last year and was named to the Eastern League All-Star team. He was the Phillies 17th-best prospect in 2011, according to Baseball America.

Welty, 25, hit .333 with 13 homers and 55 RBIs in 213 at-bats over four levels last year, maxing out at Double-A, where he hit .286 in 37 games.